Method and apparatus for coding video having temporal scalability, and method and apparatus for decoding video having temporal scalability

ABSTRACT

Provided are a video encoding method and apparatus having temporal scalability, and a video decoding method and apparatus having temporal scalability. The video encoding method includes: splitting pictures included in a picture sequence into temporal sub-layers; classifying, as a first temporal layer access picture or a second temporal layer access picture, a temporal layer access picture based on whether a picture encoded after the temporal layer access picture is capable of referring to a picture encoded before the temporal layer access picture; and adding, to transmission unit data including the temporal layer access picture, type syntax information for identifying the first temporal layer access picture and the second temporal layer access picture, wherein the picture encoded after the temporal layer access picture belongs to a same temporal sub-layer as the temporal layer access picture or belongs to an upper temporal sub-layer to the temporal layer access picture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/412,828, filed on Jan. 5, 2015, which is a National Stage applicationunder 35 U.S.C. § 371 of PCT/KR2013/005923, filed on Jul. 3, 2013, whichclaims the benefit of U.S. Provisional Application No. 61/667,654, filedon Jul. 3, 2012, all the disclosures of which are incorporated herein intheir entireties by reference.

BACKGROUND 1. Field

Apparatuses and methods consistent with exemplary embodiments relate toencoding and decoding a video, and more particularly, to video encodingand decoding methods and apparatuses having temporal scalability.

2. Description of the Related Art

Video codecs, such as ITU-T H.261, ISO/IEC MPEG-1 visual, ITU-T H.262(ISO/IEC MPEG-2 visual), ITU-T H.264, ISO/IEC MPEG-4 visual, and ITU-TH.264 (ISO/IEC MPEG-4 AVC), perform prediction encoding on a macroblockvia inter prediction or intra prediction, and generate and output abitstream according to a predetermined format defined by each videocodec, by using encoded image data.

According to a related art, a video having temporal scalability isprovided by applying a hierarchical B-picture or motion compensatedtemporal filtering (MCTF).

SUMMARY

According to aspects of one or more exemplary embodiments, videocompression efficiency may be increased as a picture encoded after atemporal layer access picture accessed during temporal layer switchingmay use a picture encoded before the temporal layer access picture as areference picture.

Furthermore, according to aspects of one or more exemplary embodiments,transmission unit data of a temporal layer access picture andtransmission unit data of a picture that is not decodable duringtemporal layer switching may be distinguished from each other in anetwork adaptive layer (NAL) unit.

According to an aspect of an exemplary embodiment, a temporal layeraccess picture is classified by distinguishing when a picture, which isreferable by pictures decoded after the temporal layer access picture,is limited and is not limited, and information for identifying theclassified temporal layer access picture is added to a transmission dataunit.

According to an aspect of an exemplary embodiment, there is provided avideo encoding method having temporal scalability, the video encodingmethod including: splitting pictures included in a picture sequence intotemporal sub-layers; classifying, as a first temporal layer accesspicture or a second temporal layer access picture, a temporal layeraccess picture based on whether a picture encoded after the temporallayer access picture is capable of referring to a picture encoded beforethe temporal layer access picture; and adding, to transmission unit datacomprising the temporal layer access picture, type syntax informationfor identifying the first temporal layer access picture and the secondtemporal layer access picture, wherein the picture encoded after thetemporal layer access picture belongs to a same temporal sub-layer asthe temporal layer access picture or belongs to an upper temporalsub-layer to the temporal layer access picture.

According to an aspect of another exemplary embodiment, there isprovided a video encoding apparatus having temporal scalability, thevideo encoding apparatus including: a video encoder configured to splitpictures included in a picture sequence into temporal sub-layers; and amultiplexer configured to classify, as a first temporal layer accesspicture or a second temporal layer access picture, a temporal layeraccess picture based on whether a picture encoded after the temporallayer access picture is capable of referring to a picture encoded beforethe temporal layer access picture, and configured to add, totransmission unit data comprising the temporal layer access picture,type syntax information for identifying the first temporal layer accesspicture and the second temporal layer access picture, wherein thepicture encoded after the temporal layer access picture belongs to asame temporal sub-layer as the temporal layer access picture or belongsto an upper temporal sub-layer to the temporal layer access picture.

According to an aspect of another exemplary embodiment, there isprovided a video decoding method having temporal scalability, the videodecoding method including: receiving transmission unit data obtained bysplitting and encoding pictures included in a picture sequence intotemporal sub-layers; and identifying, by using type syntax informationincluded in the transmission unit data, a temporal layer access pictureaccessed for temporal layer up-switching from a lower temporal sub-layerto an upper temporal sub-layer, wherein the temporal layer accesspicture is classified as a first temporal layer access picture or asecond temporal layer access picture based on whether a picture decodedafter the temporal layer access picture is capable of referring to apicture decoded before the temporal layer access picture, and whereinthe picture decoded after the temporal layer access picture belongs to asame temporal sub-layer as the temporal layer access picture or belongsto an upper temporal sub-layer to the temporal layer access picture.

According to an aspect of another exemplary embodiment, there isprovided a video decoding apparatus having temporal scalability, thevideo decoding apparatus including: a receiver configured to receivetransmission unit data obtained by splitting and encoding picturesincluded in a picture sequence into temporal sub-layers; and an inversemultiplexer configured to identify, by using type syntax informationincluded in the transmission unit data, a temporal layer access pictureaccessed for temporal layer up-switching from a lower temporal sub-layerto an upper temporal sub-layer, wherein the temporal layer accesspicture is classified as a first temporal layer access picture or asecond temporal layer access picture based on whether a picture decodedafter the temporal layer access picture is capable of referring to apicture decoded before the temporal layer access picture, and whereinthe picture decoded after the temporal layer access picture belongs to asame temporal sub-layer as the temporal layer access picture or belongsto an upper temporal sub-layer to the temporal layer access picture.

According to aspects of one or more exemplary embodiments, anunnecessary process of decoding a picture may be skipped and hardwareresources may be saved by identifying and discarding a network adaptivelayer (NAL) unit with respect to a picture that is unable to be decodedafter a temporal layer access picture. Also, according to aspects of oneor more exemplary embodiments, video compression efficiency may beincreased as a picture encoded after a temporal layer access picture mayuse a picture encoded before the temporal layer access picture as areference picture.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a video encoding apparatus according to anexemplary embodiment;

FIG. 2 is a block diagram of a video decoding apparatus according to anexemplary embodiment;

FIG. 3 is a diagram illustrating a concept of coding units according toan exemplary embodiment;

FIG. 4 is a block diagram of an image encoder based on coding units,according to an exemplary embodiment;

FIG. 5 is a block diagram of an image decoder based on coding units,according to an exemplary embodiment;

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment;

FIG. 7 is a diagram illustrating a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 8 is a diagram illustrating encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 10, 11, and 12 are diagrams illustrating a relationship betweencoding units, prediction units, and frequency transformation units,according to an exemplary embodiment;

FIG. 13 is a diagram illustrating a relationship between a coding unit,a prediction unit, and a transformation unit, according to encoding modeinformation of Table 1;

FIG. 14 is a diagram of a video encoding apparatus having temporalscalability, according to an exemplary embodiment;

FIG. 15 is a diagram of pictures included in a picture sequence, whichare split into temporal sub-layers, according to an exemplaryembodiment;

FIG. 16 is a diagram of pictures displayed according to a frame rate,according to an exemplary embodiment;

FIG. 17 is a diagram for describing a leading picture and a firsttemporal layer access, according to an exemplary embodiment;

FIG. 18 is a diagram for describing a leading picture that is unable tobe decoded during temporal layer up-switching, according to an exemplaryembodiment;

FIG. 19 is a diagram of a network adaptive layer (NAL) unit according toan exemplary embodiment;

FIG. 20 is a flowchart illustrating a video encoding method havingtemporal scalability, according to an exemplary embodiment;

FIG. 21 is a diagram of a video decoding apparatus having temporalscalability, according to exemplary embodiment; and

FIG. 22 is a flowchart illustrating a video decoding method havingtemporal scalability, according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, one or more exemplary embodiments will be described morefully with reference to the accompanying drawings. While describing oneor more exemplary embodiments, an image may include a still image or amoving image, and may also be referred to as a video. Also, whiledescribing one or more exemplary embodiments, an image frame may also bereferred to as a picture. As used herein, the term “and/or” includes anyand all combinations of one or more associated items. Expressions suchas “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

FIG. 1 is a block diagram of a video encoding apparatus 100 according toan exemplary embodiment.

A video encoding apparatus 100 according to an exemplary embodimentincludes a maximum coding unit splitter 110, a coding unit determiner120, and an output unit 130 (e.g., outputter).

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit that is a coding unit having a maximum size forthe current picture of an image. If the current picture is larger thanthe maximum coding unit, image data of the current picture may be splitinto the at least one maximum coding unit. The maximum coding unitaccording to an exemplary embodiment may be a data unit having a size of32×32, 64×64, 128×128, or 256×256, wherein a shape of the data unit is asquare having a width and length in squares of 2. The image data may beoutput to the coding unit determiner 120 according to the at least onemaximum coding unit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes a number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth increases, deeper coding units according to depths may be splitfrom the maximum coding unit to a minimum coding unit. A depth of themaximum coding unit is an uppermost depth and a depth of the minimumcoding unit is a lowermost depth. Since a size of a coding unitcorresponding to each depth decreases as the depth of the maximum codingunit increases, a coding unit corresponding to an upper depth mayinclude a plurality of coding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit a totalnumber of times a height and a width of the maximum coding unit arehierarchically split may be previously set.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output final encoding resultsaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having a leastencoding error. The determined coded depth and the image data accordingto the maximum coding unit are output to the output unit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or less thanthe maximum depth, and encoding results are compared based on each ofthe deeper coding units. A depth having the least encoding error may beselected after comparing encoding errors of the deeper coding units. Atleast one coded depth may be selected for each maximum coding unit.

A size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and a number of coding unitsincreases. Also, even if coding units correspond to the same depth inone maximum coding unit, it is determined whether to split each of thecoding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the data of each coding unit, separately.Accordingly, even when data is included in one maximum coding unit, theencoding errors according to depths may differ according to regions, andthus the coded depths may differ according to regions. Thus, one or morecoded depths may be set for one maximum coding unit, and the data of themaximum coding unit may be divided according to coding units of the oneor more coded depths.

Accordingly, the coding unit determiner 120 according to an exemplaryembodiment may determine coding units having a tree structure includedin a current maximum coding unit. The ‘coding units having a treestructure’ according to an exemplary embodiment include coding unitscorresponding to a depth determined to be a coded depth, from among alldeeper coding units included in the maximum coding unit. A coding unitof a coded depth may be hierarchically determined according to depths inthe same region of the maximum coding unit, and may be independentlydetermined in different regions. Similarly, a coded depth in a currentregion may be independently determined from a coded depth in anotherregion.

A maximum depth according to an exemplary embodiment is an index relatedto a number of times splitting is performed from a maximum coding unitto a minimum coding unit. A first maximum depth according to anexemplary embodiment may denote a total number of times splitting isperformed from the maximum coding unit to the minimum coding unit. Asecond maximum depth according to an exemplary embodiment may denote atotal number of depth levels from the maximum coding unit to the minimumcoding unit. For example, when a depth of the maximum coding unit is 0,a depth of a coding unit in which the maximum coding unit is split oncemay be set to 1, and a depth of a coding unit in which the maximumcoding unit is split twice may be set to 2. In this case, if the minimumcoding unit is a coding unit obtained by splitting the maximum codingunit four times, 5 depth levels of depths 0, 1, 2, 3, and 4 exist, andthus the first maximum depth may be set to 4 and the second maximumdepth may be set to 5.

Prediction encoding and frequency transformation may be performedaccording to the maximum coding unit. The prediction encoding and thetransformation are also performed based on the deeper coding unitsaccording to a depth equal to or depths less than the maximum depth,according to the maximum coding unit.

Since a number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the frequency transformation has to be performedon all of the deeper coding units generated as the depth increases. Forconvenience of description, the prediction encoding and the frequencytransformation will now be described based on a coding unit of a currentdepth, from among at least one maximum coding unit.

The video encoding apparatus 100 according to an exemplary embodimentmay variously select a size or shape of a data unit for encoding theimage data. In order to encode the image data, operations, such asprediction encoding, frequency transformation, and entropy encoding, areperformed, and at this time, the same data unit may be used for alloperations or different data units may be used for each operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split into coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit and a data unit obtained by splitting at least one ofa height and a width of the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split, the coding unit may become a prediction unit of2N×2N and a size of a partition may be 2N×2N, 2N×N, N×2N, or N×N.Examples of a partition type include symmetrical partitions that areobtained by symmetrically splitting a height or width of the predictionunit, partitions obtained by asymmetrically splitting the height orwidth of the prediction unit, such as 1:n or n:1, partitions that areobtained by geometrically splitting the prediction unit, and partitionshaving arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 according to an exemplary embodimentmay also perform the frequency transformation on the image data in acoding unit based not only on the coding unit for encoding the imagedata but also based on a data unit that is different from the codingunit.

In order to perform the frequency transformation in the coding unit, thefrequency transformation may be performed based on a data unit having asize smaller than or equal to the coding unit. For example, the dataunit for the frequency transformation may include a data unit for anintra mode and a data unit for an inter mode.

A data unit used as a base of the frequency transformation will now bereferred to as a ‘transformation unit’. Similarly to the coding unit,the transformation unit in the coding unit may be recursively split intosmaller sized transformation units, and thus, residual data in thecoding unit may be divided according to the transformation unit having atree structure according to transformation depths.

A transformation depth indicating a number of times splitting isperformed to reach the transformation unit by splitting the height andwidth of the coding unit may also be set in the transformation unitaccording to an exemplary embodiment. For example, in a current codingunit of 2N×2N, a transformation depth may be 0 when the size of atransformation unit is 2N×2N, may be 1 when the size of a transformationunit is N×N, and may be 2 when the size of a transformation unit isN/2×N/2. That is, the transformation unit having the tree structure mayalso be set according to transformation depths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and frequencytransformation. Accordingly, the coding unit determiner 120 not onlydetermines a coded depth having a least encoding error but alsodetermines a partition type in a prediction unit, a prediction modeaccording to prediction units, and a size of a transformation unit forfrequency transformation.

Coding units having a tree structure in a maximum coding unit and amethod of determining a partition according to an exemplary embodimentwill be described in detail below with reference to FIGS. 3 through 12.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion (RD)Optimization based on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, the partition type in theprediction unit, the prediction mode, and the size of the transformationunit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth, theencoding is performed on the current coding unit of the current depth,and thus the split information may be defined not to split the currentcoding unit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the data of the maximum coding unit may bedifferent according to locations since the data is hierarchically splitaccording to depths, and thus information about the coded depth and theencoding mode may be set for the data.

Accordingly, the output unit 130 according to an exemplary embodimentmay assign encoding information about a corresponding coded depth and anencoding mode to at least one of the coding unit, the prediction unit,and a minimum unit included in the maximum coding unit.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting alowermost depth by 4. Alternatively, the minimum unit may be a maximumrectangular data unit that may be included in all of the coding units,prediction units, partition units, and transformation units included inthe maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to deeper codingunits according to depths, and encoding information according toprediction units. The encoding information according to the deepercoding units according to depths may include the information about theprediction mode and about the size of the partitions. The encodinginformation according to the prediction units may include informationabout an estimated direction of an inter mode, about a reference imageindex of the inter mode, about a motion vector, about a chroma componentof an intra mode, and about an interpolation method of the intra mode.Also, information about a maximum size of the coding unit definedaccording to pictures, slices, or group of pictures (GOPs), andinformation about a maximum depth may be inserted into a header of abitstream.

The maximum coding unit splitter and the coding unit determiner 120correspond to a video coding layer (VCL) that determines a referenceframe of each image frame forming an image sequence by performing motionprediction and compensation according to coding units with respect tothe each image frame of the image sequence, and encode the each imageframe by using the determined reference frame.

In the video encoding apparatus 100 according to an exemplaryembodiment, the deeper coding unit is a coding unit obtained by dividinga height or width of a coding unit of an upper depth, which is one layerabove, by two. In other words, when the size of the coding unit of thecurrent depth is 2N×2N, the size of the coding unit of the lower depthis N×N. Also, the coding unit of the current depth having the size of2N×2N may include a maximum number of 4 coding units of the lower depth.

Accordingly, the video encoding apparatus 100 according to an exemplaryembodiment may form the coding units having the tree structure bydetermining coding units having an optimum shape and an optimum size foreach maximum coding unit, based on the size of the maximum coding unitand the maximum depth determined considering characteristics of thecurrent picture. Also, since encoding may be performed on each maximumcoding unit by using any one of various prediction modes and frequencytransformations, an optimum encoding mode may be determined consideringimage characteristics of the coding unit of various image sizes.

Thus, if an image having high resolution or a large data amount isencoded in a related art macroblock, a number of macroblocks per pictureexcessively increases. Accordingly, a number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the video encoding apparatusaccording to an exemplary embodiment, image compression efficiency maybe increased since a coding unit is adjusted while consideringcharacteristics of an image while increasing a maximum size of a codingunit while considering a size of the image.

FIG. 2 is a block diagram of a video decoding apparatus 200 according toan exemplary embodiment.

A video decoding apparatus 200 includes a receiver 210, an image dataand encoding information extractor 220, and an image data decoder 230.Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for various operations of the video decoding apparatus200 are identical to those described with reference to FIG. 1 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having the tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoded depth, and information about an encoding mode according to eachcoded depth may include information about a partition type of acorresponding coding unit corresponding to the coded depth, a predictionmode, and a size of a transformation unit. Also, split informationaccording to depths may be extracted as the information about the codeddepth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a least encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to an encodingmode that generates the least encoding error.

Since encoding information about the coded depth and the encoding modeaccording to an exemplary embodiment may be assigned to a predetermineddata unit from among a corresponding coding unit, a prediction unit, anda minimum unit, the image data and encoding information extractor 220may extract the information about the coded depth and the encoding modeaccording to the predetermined data units. When the information aboutthe coded depth of the corresponding maximum coding unit and theencoding mode is recorded according to the predetermined data units, thepredetermined data units having the same information about the codeddepth and the encoding mode may be inferred to be the data unitsincluded in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include prediction includingintra prediction and motion compensation, and inverse frequencytransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

Also, the image data decoder 230 may perform inverse frequencytransformation according to each transformation unit in the coding unit,based on the information about the size of the transformation unit ofthe coding unit according to coded depths, so as to perform the inversefrequency transformation according to maximum coding units.

The image data decoder 230 may determine a coded depth of a currentmaximum coding unit by using split information according to depths. Ifthe split information indicates that image data is no longer split inthe current depth, the current depth is a coded depth. Accordingly, theimage data decoder 230 may decode encoded data of the current depth byusing the information about the partition type of the prediction unit,the prediction mode, and the size of the transformation unit for imagedata of the current maximum coding unit.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode.

The video decoding apparatus 200 according to an exemplary embodimentmay obtain information about a coding unit that generates the leastencoding error when encoding is recursively performed for each maximumcoding unit, and may use the information to decode the current picture.In other words, the coding units having the tree structure determined tobe the optimum coding units in each maximum coding unit may be decoded.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restoredaccording to a size of a coding unit and an encoding mode, which areadaptively determined according to characteristics of an image, by usinginformation about an optimum encoding mode received from an encoder.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit according to an exemplaryembodiment will now be described with reference to FIGS. 3 through 13.

FIG. 3 is a diagram for describing a concept of hierarchical codingunits according to an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and examplesof the size of the coding unit may include 64×64, 32×32, 16×16, and 8×8.A coding unit of 64×64 may be split into partitions of 64×64, 64×32,32×64, or 32×32, and a coding unit of 32×32 may be split into partitionsof 32×32, 32×16, 16×32, or 16×16, a coding unit of 16×16 may be splitinto partitions of 16×16, 16×8, 8×16, or 8×8, and a coding unit of 8×8may be split into partitions of 8×8, 8×4, 4×8, or 4×4.

In video data 310, a resolution is set to 1920×1080, a maximum size of acoding unit is set to 64, and a maximum depth is set to 2. In video data320, a resolution is set to 1920×1080, a maximum size of a coding unitis set to 64, and a maximum depth is set to 3. In video data 330, aresolution is set to 352×288, a maximum size of a coding unit is set to16, and a maximum depth is set to 1. The maximum depth shown in FIG. 3denotes a total number of splits from a maximum coding unit to a minimumdecoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are increased to two layers by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are increased to one layer by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are increased to 3 layers by splitting the maximumcoding unit three times. As a depth increases, detailed information maybe more precisely expressed.

FIG. 4 is a block diagram of an image encoder 400 based on coding units,according to an exemplary embodiment.

An image encoder 400 according to an exemplary embodiment performsoperations of the coding unit determiner 120 of the video encodingapparatus 100 to encode image data. In other words, an intra predictor410 performs intra prediction on coding units in an intra mode, fromamong a current frame 405, and a motion estimator 420 and a motioncompensator 425 perform inter estimation and motion compensation oncoding units in an inter mode from among the current frame 405 by usingthe current frame 405 and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a frequency transformer 430 and a quantizer 440. Thequantized transformation coefficient is restored as data in a spatialdomain through an inverse quantizer 460 and an inverse frequencytransformer 470, and the restored data in the spatial domain is outputas the reference frame 495 after being post-processed through adeblocking unit 480 (e.g., deblocker) and a loop filtering unit 490(e.g., loop filterer). The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100 according to an exemplary embodiment, all elements of theimage encoder 400, i.e., the intra predictor 410, the motion estimator420, the motion compensator 425, the frequency transformer 430, thequantizer 440, the entropy encoder 450, the inverse quantizer 460, theinverse frequency transformer 470, the deblocking unit 480, and the loopfiltering unit 490 have to perform operations based on each coding unitfrom among coding units having a tree structure while considering themaximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 have to determine partitions and a predictionmode of each coding unit from among the coding units having the treestructure while considering the maximum size and the maximum depth of acurrent maximum coding unit, and the frequency transformer 430 has todetermine the size of the transformation unit in each coding unit fromamong the coding units having the tree structure.

FIG. 5 is a block diagram of an image decoder 500 based on coding units,according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. In FIG. 5,the parser 510 and an entropy decoder 520 are illustrated as individualcomponents, but obtaining of image data and obtaining of syntaxinformation related to encoded image data, which are performed by theparser 510, may alternatively performed by the entropy decoder 520.

The encoded image data is output as inverse quantized data through theentropy decoder 520 and an inverse quantizer 530, and the inversequantized data is restored to image data in a spatial domain through aninverse frequency transformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

Image frame data restored through the intra predictor 550 and the motioncompensator 560 may be post-processed through the deblocking unit 570(e.g., deblocker) and output to a decoded picture buffer (DPB) 580. TheDPB 580 stores a decoded image frame so as to store a reference frame,change a display order of image frames, and output an image frame. TheDPB 580 stores the decoded image frame and sets a maximum size of abuffer required for normal decoding of an image sequence, by using amaximum decoded frame buffering syntax (max_dec_frame buffering)indicating a maximum buffer size required to normally decode an imageframe output from the parser 510 or the entropy decoder 520.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, an image decoder 500 according to anexemplary embodiment may perform operations that are performed afteroperations of the parser 510 are performed.

In order for the image decoder 500 to be applied in the video decodingapparatus 200 according to an exemplary embodiment, all elements of theimage decoder 500, i.e., the parser 510, the entropy decoder 520, theinverse quantizer 530, the inverse frequency transformer 540, the intrapredictor 550, the motion compensator 560, and the deblocking unit 570,may perform decoding operations based on coding units having a treestructure for each maximum coding unit. Specifically, the intrapredictor 550 and the motion compensator 560 may determine partitionsand a prediction mode for each of the coding units having the treestructure, and the inverse frequency transformer 540 may determine asize of a transformation unit for each coding unit.

FIG. 6 is a diagram illustrating deeper coding units according to depthsand partitions, according to an exemplary embodiment.

The video encoding apparatus 100 according to an exemplary embodimentand the video decoding apparatus 200 according to an exemplaryembodiment use hierarchical coding units so as to considercharacteristics of an image. A maximum height, a maximum width, and amaximum depth of coding units may be adaptively determined according tothe characteristics of the image, or may be differently set by a user.Sizes of deeper coding units according to depths may be determinedaccording to the maximum size of the coding unit which is previouslyset.

In a hierarchical structure 600 of coding units according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. Since a depthincreases along a vertical axis of the hierarchical structure 600 of thecoding units according to an exemplary embodiment, a height and a widthof the deeper coding unit are each split. Also, a prediction unit andpartitions, which are bases for prediction encoding of each deepercoding unit, are shown along a horizontal axis of the hierarchicalstructure 600 of the coding units.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600 of the coding units, wherein a depth is 0 anda size, i.e., a height by width, is 64×64. The depth increases along thevertical axis, and a coding unit 620 having a size of 32×32 and a depthof 1, a coding unit 630 having a size of 16×16 and a depth of 2, acoding unit 640 having a size of 8×8 and a depth of 3, and a coding unit650 having a size of 4×4 and a depth of 4 exist. The coding unit 650having the size of 4×4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsincluded in the coding unit 610, i.e., a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e., a partition 620 having a size of 32×32,partitions 622 having a size of 32×16, partitions 624 having a size of16×32, and partitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e., a partition having a size of 16×16 included inthe coding unit 630, partitions 632 having a size of 16×8, partitions634 having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e., a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

Finally, the coding unit 650 having the size of 4×4 and the depth of 4is the minimum coding unit and a coding unit of a lowermost depth. Aprediction unit of the coding unit 650 is only assigned to a partitionhaving a size of 4×4.

In order to determine a coded depth of the maximum coding unit 610, thecoding unit determiner 120 of the video encoding apparatus 100 accordingto an exemplary embodiment has to perform encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth increases. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 have to be eachencoded.

In order to perform encoding according to each depth, a representativeencoding error that is a least encoding error in the corresponding depthmay be selected by performing encoding for each prediction unit in thedeeper coding units, along the horizontal axis of the hierarchicalstructure 600 of the coding units. Alternatively, the least encodingerror may be searched for by comparing representative encoding errorsaccording to depths by performing encoding for each depth as the depthincreases along the vertical axis of the hierarchical structure 600 ofthe coding units. A depth and a partition having the least encodingerror in the maximum coding unit 610 may be selected as the coded depthand a partition type of the maximum coding unit 610.

FIG. 7 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment.

The video encoding apparatus 100 according to an exemplary embodiment orthe video decoding apparatus 200 according to an exemplary embodimentencodes or decodes an image according to coding units having sizessmaller than or equal to a maximum coding unit for each maximum codingunit. Sizes of transformation units for frequency transformation duringencoding may be selected based on data units that are not larger than acorresponding coding unit.

For example, in the video encoding apparatus 100 according to anexemplary embodiment or the video decoding apparatus 200 according to anexemplary embodiment, if a size of a current coding unit 710 is 64×64,frequency transformation may be performed by using a transformationunits 720 having a size of 32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the frequency transformation on each of thetransformation units having the size of 32×32, 16×16, 8×8, and 4×4,which are smaller than 64×64, and then a transformation unit having aleast error may be selected.

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 according to anexemplary embodiment may encode and transmit information 800 about apartition type, information 810 about a prediction mode, and information820 about a size of a transformation unit for each coding unitcorresponding to a coded depth, as information about an encoding mode.

The information 800 about the partition type indicates information abouta shape of a partition obtained by splitting a prediction unit of acurrent coding unit, wherein the partition is a data unit for predictionencoding the current coding unit. For example, a current coding unitCU_0 having a size of 2N×2N may be split into any one of a partition 802having a size of 2N×2N, a partition 804 having a size of 2N×N, apartition 806 having a size of N×2N, and a partition 808 having a sizeof N×N. Here, the information 800 about the partition type of thecurrent coding unit is set to indicate one of the partition 804 having asize of 2N×N, the partition 806 having a size of N×2N, and the partition808 having a size of N×N

The information 810 about the prediction mode indicates a predictionmode of each partition. For example, the information 810 about theprediction mode may indicate a mode of prediction encoding performed ona partition indicated by the information 800, i.e., an intra mode 812,an inter mode 814, or a skip mode 816.

Also, the information 820 about the size of the transformation unitindicates a transformation unit to be based on when frequencytransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second intra transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 according to an exemplary embodiment may extractand use the information 800 about the partition type, the information810 about the prediction mode, and the information 820 about the size ofthe transformation unit for decoding according to each deeper codingunit

FIG. 9 is a diagram of deeper coding units according to depths accordingto an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 9 only illustrates thepartition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding has to be repeatedly performed on one partitionhaving a size of 2N_0×2N_0, two partitions having a size of 2N_0×N_0,two partitions having a size of N_0×2N_0, and four partitions having asize of N_0×N_0, according to each partition type. The predictionencoding in an intra mode and an inter mode may be performed on thepartitions having the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, andN_0×N_0. The prediction encoding in a skip mode may be performed only onthe partition having the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition types 912through 916 having the sizes of 2N_0×2N_0, 2N_0×N_0, and N_0×2N_0, theprediction unit 910 may be no longer split to a lower depth.

If the encoding error is the smallest in the partition type 918 havingthe size of N_0×N_0, a depth may be changed from 0 to 1 to split thepartition type 918 in operation 920, and encoding may be repeatedlyperformed on coding units 930 having a depth of 2 and a size of N_0×N_0to search for a least encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948 havingthe size of N_1×N_1, a depth may be changed from 1 to 2 to split thepartition type 948 in operation 950, and encoding may be repeatedlyperformed on coding units 960, which have a depth of 2 and a size ofN_2×N_2 to search for a least encoding error.

When a maximum depth is d, split information according to each depth maybe set until a depth becomes d-1, and split information may be set untila depth becomes d-2. In other words, when encoding is performed untilthe depth is d-1 after a coding unit corresponding to a depth of d-2 issplit in operation 970, a prediction unit 990 for prediction encoding acoding unit 980 having a depth of d-1 and a size of 2N_(d-1)×2N_(d-1)may include partitions of a partition type 992 having a size of2N_(d-1)×2N_(d-1), a partition type 994 having a size of2N_(d-1)×N_(d-1), a partition type 996 having a size ofN_(d-1)×2N_(d-1), and a partition type 998 having a size ofN_(d-1)×N_(d-1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d-1)×2N_(d-1), two partitions having a size of2N_(d-1)×N_(d-1), two partitions having a size of N_(d-1)×2N_(d-1), fourpartitions having a size of N_(d-1)×N_(d-1) from among the partitiontypes 992 through 998 to search for a partition type having a leastencoding error.

Even when the partition type 998 having the size of N_(d-1)×N_(d-1) hasthe least encoding error, since a maximum depth is d, a coding unitCU_(d-1) having a depth of d-1 may be no longer split to a lower depth,a coded depth for a current maximum coding unit 900 may be determined tobe d-1, and a partition type of the current maximum coding unit 900 maybe determined to be N_(d-1)×N_(d-1). Also, since the maximum depth is d,split information for a coding unit 952 having a depth of d-1 is notset.

A data unit 999 may be referred to as a ‘minimum unit’ for the currentmaximum coding unit. A minimum unit according to an exemplary embodimentmay be a rectangular data unit obtained by splitting a minimum codingunit having a lowermost coded depth by 4. By performing the encodingrepeatedly, the video encoding apparatus 100 may select a depth having aleast encoding error by comparing encoding errors according to depths ofthe coding unit 900 to determine a coded depth, and may set acorresponding partition type and a prediction mode as an encoding modeof the coded depth.

As such, the least encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit has to be split from a depth of 0 to the coded depth, only splitinformation of the coded depth has to be set to 0, and split informationof depths excluding the coded depth has to be set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 according to an exemplary embodiment may extractand use the information about the coded depth and the prediction unit ofthe coding unit 900 to decode the coding unit 912. The video decodingapparatus 200 according to an exemplary embodiment may determine adepth, in which split information is 0, as a coded depth by using splitinformation according to depths, and may use information about anencoding mode of the corresponding depth for decoding.

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units, prediction units, and frequency transformation units,according to an exemplary embodiment.

Coding units 1010 are coding units corresponding to coded depthsdetermined by the video encoding apparatus 100 according to an exemplaryembodiment, in a maximum coding unit. Prediction units 1060 arepartitions of prediction units of each of the coding units 1010, andtransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some partitions 1014, 1016, 1022, 1032,1048, 1050, 1052, and 1054 are obtained by splitting the coding units.In other words, partition types in the partitions 1014, 1022, 1050, and1054 have a size of 2N×N, partition types in the partitions 1016, 1048,and 1052 have a size of N×2N, and a partition type of the partition 1032has a size of N×N. Prediction units and partitions of the coding units1010 are smaller than or equal to each coding unit.

Frequency transformation or inverse frequency transformation isperformed on image data of the transformation unit 1052 in thetransformation units 1070 in a data unit that is smaller than thetransformation unit 1052. Also, the transformation units 1014, 1016,1022, 1032, 1048, 1050, and 1052 in the transformation units 1070 aredifferent from those in the prediction units 1060 in terms of sizes orshapes. In other words, the video encoding apparatus 100 according to anexemplary embodiment and the video decoding apparatus 200 according toan exemplary embodiment may perform intra prediction/motionestimation/motion compensation, and frequency transformation/inversefrequency transformation individually on a data unit even in the samecoding unit.

Accordingly, encoding may be recursively performed on each of codingunits having a hierarchical structure in each region of a maximum codingunit to determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding apparatus 100according to an exemplary embodiment and the video decoding apparatus200 according to an exemplary embodiment.

TABLE 1 Split Information 0 (Encoding on Coding Unit having Size of 2N ×2N and Current Depth of d) Partition Type Size of Transformation UnitSymmetrical Asymmetrical Split Information 0 Split Information 1Prediction Partition Partition of Transformation of Transformation SplitMode Type Type Unit Unit Information 1 Intra 2N × 2N 2N × nU 2N × 2N N ×N Repeatedly Inter 2N × N  2N × nD (Symmetrical Encode Skip  N × 2N  nL× 2N Partition Coding (Only N × N nR × 2N Type) Units 2N × 2N) N/2 × N/2having (Asymmetrical Lower Partition Depth of Type) d + 1

The output unit 130 of the video encoding apparatus 100 according to anexemplary embodiment may output the encoding information about thecoding units having the tree structure, and the image data and encodinginformation extractor 220 of the video decoding apparatus 200 accordingto an exemplary embodiment may extract the encoding information aboutthe coding units having the tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split to alower depth, is a coded depth, and thus information about a partitiontype, a prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding has to be independentlyperformed on four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode may be defined only in a partition type havinga size of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD are respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N arerespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit is set to 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be set to N×N, and if the partition type of thecurrent coding unit is an asymmetrical partition type, the size of thetransformation unit may be set to N/2×N/2.

The encoding information about coding units having a tree structureaccording to an exemplary embodiment may be assigned to at least one ofa coding unit corresponding to a coded depth, a prediction unit, and aminimum unit. The coding unit corresponding to the coded depth mayinclude at least one of a prediction unit and a minimum unit containingthe same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth may be determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted by referring toadjacent data units, encoding information of data units in deeper codingunits adjacent to the current coding unit may be directly referred toand used.

Alternatively, if a current coding unit is prediction encoded byreferring to adjacent data units, data units adjacent to the currentcoding unit in deeper coding units may be searched for by using encodedinformation of the data units, and the searched adjacent coding unitsmay be referred to for prediction encoding the current coding unit.

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according to theencoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

When the partition type is set to be symmetrical, i.e., the partitiontype 1322 having the size of 2N×2N, 1324 having the size of 2N×N, 1326having the size of N×2N, or 1328 having the size of N×N, atransformation unit 1342 having a size of 2N×2N may be set if splitinformation (TU size flag) of a transformation unit is 0, and atransformation unit 1344 having a size of N×N may be set if a TU sizeflag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332 having the size of 2N×nU, 1334 having the size of 2N×nD, 1336having the size of nL×2N, or 1338 having the size of nR×2N, atransformation unit 1352 having a size of 2N×2N may be set if a TU sizeflag is 0, and a transformation unit 1354 having a size of N/2×N/2 maybe set if a TU size flag is 1.

FIG. 14 is a diagram of a video encoding apparatus 1400 having temporalscalability, according to an exemplary embodiment.

Referring to FIG. 14, a video encoding apparatus 1400 according to anexemplary embodiment includes a video encoder 1410 and a multiplexer1420.

The video encoder 1410 corresponds to the video encoding apparatus 100of FIG. 1 described above, and a VCL that handles an encoding process ofvideo data encodes video data based on a hierarchical coding unit asdescribed above. The multiplexer 1420 multiplexes the video data byusing a transmission data unit suitable for a protocol or a storageformat of a communication channel or a storage media, a video editingsystem, or a media framework. As will be described below, themultiplexer 1420 may transmit the video data by using a networkabstraction layer (NAL) unit that is a transmission unit in an NAL.

In order to provide video data having temporal scalability, the videoencoder 1410 may split pictures included in a picture sequence intotemporal sub-layers. A temporal sub-layer denotes a group of NAL unitsincluding pictures having same temporal identifiers (temporal_id) orinformation about such pictures.

The multiplexer 1420 may classify a temporal layer access picture as afirst temporal layer access picture or a second temporal layer accesspicture based on whether a picture, which is encoded after the temporallayer access picture and belongs to a same or upper temporal sub-layeras or than the temporal layer access picture, is capable of referring toa picture encoded before the temporal layer access picture, and add typesyntax information for identifying the first temporal layer accesspicture and the second temporal layer access picture to transmissionunit data including the temporal layer access picture. A decoding orderand an encoding order denote an order in which pictures are processed,respectively by a decoder and an encoder, and the encoding order may bethe same as the decoding order. Thus, while describing exemplaryembodiments, the encoding order may denote a decoding order and viceversa.

The temporal layer access picture is a picture that is initially encoded(or decoded) after up-switching by being included in an upper temporalsub-layer accessed if switching occurs from a lower temporal sub-layerto the upper temporal sub-layer. As will be described below, thetemporal layer access picture is a picture that refers to an availablepicture at least when the up-switching occurs. The first temporal layeraccess picture denotes a temporal layer access picture wherein thepicture that is encoded after the temporal layer access picture andbelongs to the same or upper temporal sub-layer as or than the temporallayer access picture is capable of referring to the picture encodedbefore the temporal layer access picture. The second temporal layeraccess picture denotes a temporal layer access picture wherein thepicture, which is encoded after the temporal layer access picture andbelongs to the same or upper temporal sub-layer as or than the temporallayer access picture, is not capable of referring to the picture encodedbefore the temporal layer access picture.

FIG. 15 is a diagram of pictures included in a picture sequence, whichare split into temporal sub-layers, according to an exemplaryembodiment. In FIGS. 15 and 16, I, B, and P respectively denote anI-picture, a B-picture, and a P-picture, and a number after I, B, or Pdenotes a number in a display order. In FIG. 15, a direction of an arrowdenotes a reference direction. For example, an I0 picture 1500 is usedas a reference picture of a B1 picture 1531.

Referring to FIG. 15, the video encoder 1410 may provide video datahaving temporal scalability by classifying I0 through B7 pictures 1500through 1534 included in picture sequences into temporal sub-layers andassigning temporal_id to the pictures I0 through B7 pictures 1500through 1534 included in each temporal sub-layer.

In detail, values of temporal_id of the I0 picture 1500 and the P8picture 1501 that belong to a lowermost temporal sub-layer are set to 0.The B4 picture 1510 belongs to a temporal sub-layer having temporal_idof 1. The B2 picture 1520 and the B6 picture 1521 belong to a temporalsub-layer having temporal_id of 2. The B1 picture 1531, the B3 picture1532, the B5 picture 1533, and the B7 picture 1534 belong to a temporalsub-layer having temporal_id of 3.

FIG. 16 is a diagram of pictures displayed according to a frame rate,according to an exemplary embodiment.

Referring to FIGS. 15 and 16, when a frame rate is 7.5 Hz, an I0 pictureand a P8 picture at a lowermost temporal sub-layer and havingtemporal_id of 0 are displayed. When a frame rate is 15 Hz, a B4 picturehaving temporal_id of 1 is displayed as well as the I0 and P8 pictureshaving temporal_id of 0. When a frame rate is 30 Hz, the I0 picture, aB2 picture, the B4 picture, a B6 picture, and the P8 picture havingtemporal_id of 0, 1, and 2 are displayed. When a frame rate is 60 Hz,the I0 picture, a B1 picture, the B2 picture, a B3 picture, the B4picture, a B5 picture, the B6 picture, a B7 picture, and the P8 picturehaving temporal_id of 0, 1, 2, and 4 are displayed.

As such, temporal scalability may be realized by decoding all pictureshaving temporal_id that is lower than or equal to a predetermined valueaccording to a frame rate, and displaying the decoded pictures. In otherwords, temporal scalability may be realized by decoding and displayingpictures included in all temporal sub-layers lower than or equal to anupper temporal sub-layer having temporal_id of a predetermined valueaccording to a frame rate.

A change of a frame rate may be defined as temporal layer switching. Achange from a low frame rate to a high frame rate is defined as temporallayer up-switching, and a change from a high frame rate to a low framerate is defined as a temporal layer down-switching. Since temporal layerdown-switching may be performed by removing pictures having temporal_idhigher than a predetermined value, the temporal layer down-switching maybe performed at any time. For example, referring back to FIG. 16, when aframe rate changes from 30 Hz to 7.5 Hz, temporal layer down-switchingmay be performed by selecting and displaying only the I0 picture and theP8 picture by excluding pictures having temporal_id equal to or higherthan 1, i.e., the B2 picture, the B4 picture, and the B6 picture, fromamong the I0 picture, the B2 picture, the B4 picture, the B6 picture,and the P8 picture having temporal_id of 0, 1, and 2.

On the other hand, temporal layer up-switching is not always possible.For example, if a picture that belongs to an upper temporal sub-layerrefers to a further upper picture that is not available duringup-switching, the picture that belongs to the upper temporal sub-layeris not decodable. It is assumed that temporal layer up-switching isgenerated from a temporal sub-layer having temporal_id of 0 to an uppertemporal sub-layer having temporal_id of 1. If a picture that belongs tothe upper temporal sub-layer having temporal_id of 1 refers to a picturethat belongs to a further upper temporal sub-layer having temporal_id ofat least 2 as a reference picture, temporal sub-layer up-switching isunable to be performed.

Accordingly, a picture that refers to a picture available at leastduring temporal layer up-switching from among pictures that belong to anupper temporal sub-layer should be used as a temporal layer accesspicture.

In order to improve prediction efficiency of a picture that is encoded(or decoded) after the temporal layer access picture, a picture that isencoded after the temporal layer access picture and belongs to the sameor upper temporal sub-layer as or than the temporal layer access picturemay refer to a picture that is encoded before the temporal layer accesspicture. Here, prediction efficiency of an image may be increased byexpanding reference possibilities since it is more likely that areference picture similar to a picture to be encoded may be used if anumber of candidates available as reference pictures increases. Atemporal layer access picture that allows such reference is defined asthe first temporal layer access picture. In other words, the firsttemporal layer access picture is a temporal layer access picture thatallows the picture, which is encoded after the temporal layer accesspicture and belongs to the same or upper temporal sub-layer as or thanthe temporal layer access picture, to refer to the picture that isencoded before the temporal layer access picture. On the other hand, atemporal layer access picture that restrict such reference is defined asthe second temporal layer access picture. In other words, the secondtemporal layer access picture is a temporal layer access picture thatdoes not allow the picture, which is encoded after the temporal layeraccess picture and belongs to the same or upper temporal sub-layer as orthan the temporal layer access picture, to refer to the picture that isencoded before the temporal layer access picture.

FIG. 17 is a diagram for describing a leading picture and the firsttemporal layer access, according to an exemplary embodiment. Asdescribed above, I, B, and P respectively denote an I-picture, aB-picture, and a P-picture, and a number after I, B, and P denotes anumber in a display order. Also, a direction of an arrow denotes areference direction.

The leading picture of a predetermined picture denotes a picture that isdecoded after the predetermined picture but displayed before thepredetermined picture. Referring to FIG. 17, a B3 picture 1720 is aleading picture that is displayed before a B4 picture 1710 but decodedafter the B4 picture 1710. Here, it is assumed that the B3 picture 1720is bi-directionally predicted by referring to a B2 picture as well asthe B4 picture 1710. The B4 picture 1710 may be classified as the firsttemporal layer access picture since the B3 picture 1720 that belongs tothe same or upper temporal sub-layer and decoded after the B4 picture1710 according to a decoding order refers to the B2 picture that isdecoded before the B4 picture 1710.

As described above, a number of pictures available as a referencepicture may be increased in order to increase prediction efficiency ofan image, but in the case of the first temporal layer access picture, apicture that is not further needed during a decoding process may bedecoded according to a reference relationship between pictures duringtemporal layer up-switching.

FIG. 18 is a diagram for describing a leading picture that is unable tobe decoded during temporal layer up-switching, according to an exemplaryembodiment.

Referring to FIG. 18, it is assumed that a B4 picture 1810 is a temporallayer access picture if temporal layer up-switching is performed from alowermost temporal sub-layer to an immediately upper temporal sub-layer.Also, it is assumed that the B4 picture 1810 is the first temporal layeraccess picture, wherein a picture that is decoded after the B4 picture1810 and belongs the same or upper temporal sub-layer as or than the B4picture 1810 is capable of referring to a picture that is decoded beforethe B4 picture 1810. If the temporal layer up-switching is performed, aB3 picture 1820 that is a leading picture of the B4 picture 1810 isunable to be decoded since there is no reference picture. As such, inthe case of the first temporal layer access picture, since a picturethat is decoded later is not restricted to refer to a picture that isdecoded before the first temporal layer access picture, there may be aleading picture that is unable to be decoded later according to areference relationship between pictures.

The multiplexer 1420 of the video encoding apparatus 1400 according toan exemplary embodiment may separately classify a picture, which isunable to be decoded during temporal layer up-switching regarding arelationship with the first temporal layer access picture, as adiscardable picture and may set a predetermined syntax ‘nal_unit_type’to a header of an NAL unit to indicate the discardable picture. Forexample, the B3 picture 1820 of FIG. 18 may be classified as adiscardable picture during temporal layer up-switching.

The picture that is unable to be decoded during the temporal layerup-switching is classified as the discardable picture so that, if adecoding apparatus receives an NAL unit including a discardable picture,hardware resources may be saved by skipping a separate decoding process.

The multiplexer 1420 adds, to a header of an NAL unit including thefirst temporal layer access picture, first type syntax information(nal_unit_type) indicating that the first temporal layer access pictureis included, and adds, to a header of the transmission unit dataincluding the second temporal layer access picture, second type syntaxinformation (nal_unit_type) indicating that the second temporal layeraccess picture is included.

FIG. 19 is a diagram of an NAL unit according to an exemplaryembodiment.

Referring to FIG. 19, an NAL unit 1900 includes an NAL header 1910 and araw byte sequence payload (RBSP) 1920. An RBSP trailing bit 1930 is alength adjusting bit added behind the RBSP 1920 so as to express alength of the RBSP 1920 in multiples of 8 bits. The RBSP trailing bit1930 may start from ‘1’ and then include consecutive ‘0’s determinedbased on the length of the RBSP 1920 so as to have a pattern such as‘100 . . . ’, and by searching for ‘1’ that is an initial bit value, thelast bit location of the RBSP 1920 immediately before the ‘1’ may bedetermined.

Syntax ‘nal_unit_type’ 1912 for identifying whether the first temporallayer access picture, the second temporal layer access picture, and thediscardable picture are included in the NAL unit 1900 may be set to theNAL header 1910, as well as syntax ‘forbidden_zero_bit’ 1911 having avalue of 0. In other words, an NAL unit having intrinsic syntax‘nal_unit_type’ for transmitting the first temporal layer accesspicture, the second temporal layer access picture, and the discardablepicture may be used.

Table 2 below shows examples of the NAL unit 1900 according to a valueof syntax ‘nal_unit_type’.

TABLE 2 Content of NAL unit and RBSP syntax NAL unit nal_unit_typestructure type class 0 Unspecified non-VCL 1 Coded slice of a non-RAP,non-TFD and VCL non-TLA picture slice_layer_rbsp( ) 2 Coded slice of aTFD picture VCL slice_layer_rbsp( ) 3 Coded slice of a non-TFD TLApicture VCL slice_layer_rbsp( ) 4, 5 Coded slice of a CRA picture VCLslice_layer_rbsp( ) 6, 7 Coded slice of a BLA picture VCLslice_layer_rbsp( ) 8 Coded slice of an IDR picture VCLslice_layer_rbsp( )  9, 10 Coded slice of a BLT picture VCLslice_layer_rbsp( ) 11 to 24 Reserved n/a 25 Video parameter set non-VCLvideo_parameter_set_rbsp( ) 26 Sequence parameter set non-VCLseq_parameter_set_rbsp( ) 27 Picture parameter set non-VCLpic_parameter_set_rbsp( ) 28 Adaptation parameter set non-VCL aps_rbsp() 29 Access unit delimiter non-VCL access_unit_delimiter_rbsp( ) 30Filler data non-VCL filler_data_rbsp( ) 31 Supplemental enhancementinformation non-VCL (SEI) sei_rbsp( ) 32 to 47 Reserved n/a 48 to 63Unspecified non-VCL

Referring to Table 2, when temporal layer access pictures according toan exemplary embodiment are broken link temporal layer access (BLT)pictures, each of the first and second temporal layer access picturesmay be inserted into and transmitted with NAL units in which values ofsyntax ‘nal_unit_type’ are 6 and 7.

Also, when a discardable picture is a tagged for discard (TFD) picture,the discardable picture may be inserted into and transmitted with an NALunit in which a value of syntax ‘nal_unit_type’ is 2.

FIG. 20 is a flowchart illustrating a video encoding method havingtemporal scalability, according to an exemplary embodiment.

Referring to FIG. 20, in operation 2010, the video encoder 1410 encodespictures included in a picture sequence, and splits and outputs theencoded pictures into temporal sub-layers.

In operation 2020, the multiplexer 1420 classifies a temporal layeraccess picture as a first temporal layer access picture or a secondtemporal layer access picture based on whether a picture, which isencoded after the temporal layer access picture and belongs to a same orupper temporal sub-layer as or than the temporal layer access picture,is capable of referring to a picture encoded before the temporal layeraccess picture. As described above, the first temporal layer accesspicture denotes a temporal layer access picture that allows the picture,which is encoded after the temporal layer access picture and belongs tothe same or upper temporal sub-layer as or than the temporal layeraccess picture, to refer to the picture encoded before the temporallayer access picture. The second temporal layer access picture denotes atemporal layer access picture that does not allow the picture, which isencoded after the temporal layer access picture and belongs to the sameor upper temporal sub-layer as or than the temporal layer accesspicture, to refer to the picture encoded before the temporal layeraccess picture.

In operation 2030, the multiplexer 1420 adds type syntax information foridentifying the first temporal layer access picture and the secondtemporal layer access picture to transmission unit data including thetemporal layer access picture. As described above, the multiplexer 1420may use an NAL unit that has intrinsic syntax ‘nal_unit_type’ fortransmitting the first temporal layer access picture, the secondtemporal layer access picture, and a discardable picture.

FIG. 21 is a diagram of a video decoding apparatus having temporalscalability, according to exemplary embodiment.

Referring to FIG. 21, a video decoding apparatus 2100 according to anexemplary embodiment includes a video decoder 2130, an inversemultiplexer 2120, and a receiver 2110.

The receiver 2110 receives transmission unit data, i.e., NAL unit data,from the video encoding apparatus 1400 of FIG. 14.

The inverse multiplexer 2120 may determine a type of a picture includedin the transmission unit data by using an identifier included in thetransmission unit data. As described above, the inverse multiplexer 2120may determine the NAL unit including the first temporal layer accesspicture, the second temporal layer access picture, and the discardablepicture based on the syntax ‘nal_unit_type’.

The video decoder 2130 corresponds to the video decoding apparatus 200of FIG. 2 or the image decoder 500 of FIG. 5, and decodes a receivedpicture by obtaining split information, information about a partitiontype, information about a prediction mode, information about a size of atransformation unit, and information about a parameter set related to anencoding process with respect to coding units used to generate imagedata and encoded data.

FIG. 22 is a flowchart illustrating a video decoding method havingtemporal scalability, according to an exemplary embodiment.

Referring to FIG. 22, in operation 2210, the receiver 2110 receivestransmission unit data obtained by splitting and encoding picturesincluded in a picture sequence into temporal sub-layers.

In operation 2220, the inverse multiplexer 2120 identifies thetransmission unit data including a temporal layer access picture that isaccessed for temporal layer up-switching from a lower temporal sub-layerto an upper temporal sub-layer, by using type syntax informationincluded in the transmission unit data.

One or more exemplary embodiments may be written as computer programsand may be implemented in general-use digital computers that execute theprograms by using a computer-readable recording medium. Examples of thecomputer-readable recording medium include magnetic storage media (e.g.,a read-only memory (ROM), a floppy disc, and a hard disc), opticallyreadable media (e.g., a compact disc-read only memory (CD-ROM) and adigital versatile disc (DVD)), and carrier waves (such as datatransmission through the Internet). Furthermore, it is understood thatone or more of the above-described components, elements, units, etc.,may be implemented as hardware (e.g., as at least one of one or moreprocessors, a memory, circuitry, etc.) or software (e.g., implemented byat least one processor), or a combination of hardware and software.

While exemplary embodiments been particularly shown and described above,it will be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope of the invention as defined by the appended claims.The exemplary embodiments should be considered in a descriptive senseonly and not for purposes of limitation. Therefore, the scope of theinvention is defined not by the detailed description but by the appendedclaims, and all differences within the scope will be construed as beingincluded in the present invention.

The invention claimed is:
 1. A video decoding apparatus, the videodecoding apparatus comprising: a receiver which receives transmissionunit data; an inverse multiplexer which identifies a type of a currentpicture included in the transmission unit data, the transmission unitdata comprising a temporal layer access picture accessed for temporallayer up-switching from a lower temporal sub-layer to a higher temporalsub-layer, by using type syntax information included in the transmissionunit data; and a decoder which decodes the current picture based on theidentified type, wherein the type syntax information indicates whetherthe current picture is a first temporal layer access picture or a secondtemporal layer access picture, wherein, when the type syntax informationindicates the type of the current picture is the first temporal layeraccess picture, a first picture, which is decoded after the firsttemporal layer access picture, displayed later than the first temporallayer access picture, and belongs to a higher temporal sub-layer than atemporal sub-layer of the first temporal layer access picture, iscapable of referring to a second picture decoded before the firsttemporal layer access picture, and when the type syntax informationindicates the type of the current picture is the second temporal layeraccess picture, a third picture, which is decoded after the secondtemporal layer access picture, displayed later than the second temporallayer access picture, and belongs to a higher temporal sub-layer than atemporal sub-layer of the second temporal layer access picture, is notcapable of referring to a picture decoded before the second temporallayer access picture.
 2. A video encoding method for encoding videohaving temporal scalability, the video encoding method comprising:encoding pictures included in a picture sequence; identifying a temporallayer access picture as a first temporal layer access picture or asecond temporal layer access picture; and generating a bitstream, thebitstream comprising transmission unit data and type syntax informationindicating a type of a current picture included in the transmission unitdata, the transmission unit data comprising a temporal layer accesspicture accessed for temporal layer up-switching from a lower temporalsub-layer to a higher temporal sub-layer, wherein the type syntaxinformation indicates whether the current picture is the first temporallayer access picture or the second temporal layer access picture,wherein, when the type syntax information indicates the type of thecurrent picture is the first temporal layer access picture, a firstpicture, which is decoded after the first temporal layer access picture,displayed later than the first temporal layer access picture, andbelongs to a higher temporal sub-layer than a temporal sub-layer of thefirst temporal layer access picture, is capable of referring to a secondpicture decoded before the first temporal layer access picture, and whenthe type syntax information indicates the type of the current picture isthe second temporal layer access picture, a third picture, which isdecoded after the second temporal layer access picture, displayed laterthan the second temporal layer access picture, and belongs to a highertemporal sub-layer than a temporal sub-layer of the second temporallayer access picture, is not capable of referring to a picture decodedbefore the second temporal layer access picture.
 3. A non-transitorycomputer-readable storage medium storing a bitstream, the bitstreamcomprising transmission unit data and type syntax information indicatinga type of a current picture included in the transmission unit data, thetransmission unit data comprising a temporal layer access pictureaccessed for temporal layer up-switching from a lower temporal sub-layerto a higher temporal sub-layer, wherein the type syntax informationindicates whether the current picture is a first temporal layer accesspicture or a second temporal layer access picture, wherein, when thetype syntax information indicates the type of the current picture is thefirst temporal layer access picture, a first picture, which is decodedafter the first temporal layer access picture, displayed later than thefirst temporal layer access picture, and belongs to a higher temporalsub-layer than a temporal sub-layer of the first temporal layer accesspicture, is capable of referring to a second picture decoded before thefirst temporal layer access picture, and when the type syntaxinformation indicates the type of the current picture is the secondtemporal layer access picture, a third picture, which is decoded afterthe second temporal layer access picture, displayed later than thesecond temporal layer access picture, and belongs to a higher temporalsub-layer than a temporal sub-layer of the second temporal layer accesspicture, is not capable of referring to a picture decoded before thesecond temporal layer access picture.